Chapter I. § 1. The way in which one works when studying chemotactical phenomena is compared to the proceeding for the examination of phototropical and geotropical processes. By this it is possible to call the supposition concerning the separated sensibilities for different chemotactic active substances, premature. § 2. With the help of data from literature is pointed out, that the capillary method is not a very suitable one to get a closer insight into the nature of the chemotactical phenomena. § 3. Here is discussed, that a colloid-chemical representation can be formed of the influence of chemotactica. Chapter II. § 1. It is denoted how the algae, which served for the experiments, were cultivated. By determination was proved that the Alga used was Chlamydomonas variabilis. § 2. Here is discussed, that the terms physical process, chemical process, physiological process and stimulation process are unfit to keep apart the various phenomena from physiology. § 3. For Chlamydomonas variabilis Dangeard was observed a very clear positive geotaxis while it appears from literature, that some investigators have found Chlamydomonas pulvisculus to be negativity geotactical. § 4. Here is discussed that the reaction to gravity takes no longer place after addition of small quantities of acid, base or salt to the water, in which the algae are. § 5. Here is told, that the susceptibility of Chlamydomonas to the light, just like that to gravity under the influence of added electrolytes is diminished. Besides a negative phototactical reaction a positive reaction can occur. The solutions in which the positive phototaxis acts, always contain so great an amount of an electrolyte, that a very slight increase of concentration causes insusceptibility to the light and to gravity. § 6. The attaching of Chlamydomonas to the glass side (thigmotaxis) occurs, as the ends of the cilia stick to the glass. The thigmotactical phenomena only take place in solutions, which are not distinctly alkaline. In solutions which only contain acid, at any rate little salt, the phenomenon often occurs, when the amount of acid is nearly as large that the motility is very slight and also insusceptibility to light and to gravity acts. The individuals of Chlamydomonas can also mutually stick together with the cilia. This phenomenon can act so generally in a preparation, that it becomes also visible macroscopically. § 7. Here are discussed the substances on which Chlamydomonas reacts chemotactically. It is possibe to produce in the dark under cover-glass with Chlamydomonas an oxygen-line. This is not yet considered to be a proof, that Chlamydomonas really reacts to the oxygen of the air. Here is discussed how with the experiment under cover-glass also the carbonic acid concentration must change. By means of Spirillum species it could be shown, that under the influence of carbonic acid as a gas a removal of the oxygen-line, formed by Spirillum was caused; with nitrogen, oxygen and air, this was not possible. Chapter III. § 1. It can easily be observed, whether the organisms are very movable or only little movable. By defining limiting concentrations, it was possible to calculate ihe critical concentration, where theoretically the transition of very movable to little movable took place. The motility was judged by means of the reaction to gravity. § 2. It appeared to be necessary to let the experiments take place in little tubes with the same diameter. The influence of the temperature was of small importance. The experiments were done, exposed to one-sided diffuse day light: an attempt, to experiment in the dark, failed, since very irregular results were attained by it. § 3. Here is discussed that the algae freed from the culture-fluid were brought into the electrolyte solutions. They were washed with distilled water for a short time. The susceptibility to electrolyte solutions was not changed by this. For every experiment was used about the same number of organisms. § 4. In connection with the great influence of the H-ions and the OH-ions, it was desirable to have the solutions change regularly not only with regard to the salt concentration but also with regard to the amount of H-ions and of the OH-ions. The solutions were used in series. In every series the H-ion concentration was constant. The different series varied, as regards the hydrion concentration. By means of the series limiting concentrations were fixed and from these critical concentrations were calculated. The electrolytes are for the greater part split up into ions; it is a matter of course to attribute the influence of the electrolytes to the ions. In neutral salts the anions and the cations are always present in the same proportion. In salt solutions we always observe the influence of equal quantities of anions and cations collectively. The product of the number of H-ions and OH-ions is constant. By this it is possible to examine separately the influence of the H-ions and of the OH-ions. In consequence of this we can find in a series with constant salt concentration, but with regularly increasing H-ion concentration, two critical concentrations, while in a series with a constant H-ion concentration one critical concentration is found. § 5. The critical concentrations and the limiting concentrations are denoted in a rectangular coordinate system; on the ordinate-axis is stated the acid or base concentration and on the abscissa-axis the salt concentration. § 6. Salt solutions with regularly changing H-ion concentrations were obtained bij adding small quantities of acid or base. By this we must observe special measures of precaution. With the acetate solutions, the fluids were made acid with acetic acid. In this case we obtain ..buffer solutions”, which offers special advantages. Chapter IV. § 1. Here is discussed, that the H-ions and the OH-ions have a great influence on the motility of Chlamydomonas. To show this, we used mixtures of sodium acetate with acetic acid and with potassium hydroxyd, in which the amount of acetate was constant, whilst the H-ion concentration changed regularly. § 2. The experiments under influence of acid and alkaline solutions of K2S04, KC1 and KNOs were done sixfold, bij which the results were much more reliable. It is denoted how the critical concentration is calculated. By the use of a new culture the immediately preceding experiments were repeated to see whether the organisms of the new culture were as sensible to electrolytes as those of the old culture. Generally the differences were insignificant. For KC1 was once observed an important change of the sensibility. Here is discussed that the changed sensibility might be caused under the influence of a culture-fluid of a somewhat different composition. § 3. There is discussed that the influence of base and salt according to the course of the curve for K,S04 in most alkaline solutions is about additive, while the influence of mixtures of acid and salt cannot be additive. Acid and salt counteract one another’s influence. This also appears from the figure of sodium acetate in the most acid solutions. A similar conduct with regard to mixtures of salt and base and of salt and acid, was stated by Hardy with the dissolving of colloidal globulins, which were flocculated by small quantities of electrolytes. § 4. Here is discussed that the middle part of the curves often has a capricious out look, by the presence of maxima and minima. In general five maxima can be distinguished. Through this part of the curves an axis of symmetry can be drawn. This axis is often not horizontal. The possibility exists that the symmetry is caused, as we have to do with the action of ions. The principal direction of the middle part of the curves is influenced perhaps by the valence of the ions. The presence of the tops cannot immediately be explained. § 5. Here is shown, that the plasmcolloids can only be compared to colloids, which can behave as acid and base but further contain properties of the suspenoids. For a comparison the globulins ask for our attention. § 6. By the figures is proved that the isoelectric point (according to Michaelis) of the plasmcolloids can be expected in weakly alkaline solutions. The place of this point could not be fixed directly. § 7. Here is discussed, that there are yet two other phenomena, which might give information about the place of the isoelectric point, namely the sticking to the glass and the mutual sticking together of the algae with their cilia. The first phenomenon, however, took place in solutions, which were more acid than those, in which the plasmcolloids, according to the course of the curves are isoelectric. This is attributed to the negative charge of the glass with regard to alkaline, neutral and very weakly acid solutions. In which solutions the mutual sticking together took place, was not noted down. Besides the fact that in the sticking to the glass the influence of the charge of the boundary surface glass water plays a part, a removal of the phenomena to more acid solutions can be expected in all cases in which the motility of the algae is very great. Under the influence of the light or of gravity the algae come continually with the cilia into contact with the glass, by which loss or taking up of electrical charge can take place. We point to the fact that the acid optimum of Chlamydomonas with chemotactical experiments is perhaps an acid optimum only under the influence of the glass.