552 Btiller^—Contributions to our Knowledge of the 
upon the injurious effects of distilled water. Extremes of 
heat and exhaustion due to age have been shown 1 to diminish 
the sensitiveness of the spermatozoa to chemotactic stimuli. 
It is, therefore, almost certain that a similar diminution in 
sensitiveness Is caused by an unfavourable medium for swarm¬ 
ing. On these physiological grounds, therefore, in all my 
experiments tap-water was used as the medium into which 
the spermatozoa were liberated and distilled water avoided. 
Tap-water is, however, a weak salt solution. That used con¬ 
tained about 0-014 gm°/ 0 mixed salts 2 . All the solutions 
tested in the capillary tubes were also made with tap-water. 
The result of this was that the difference in the medium 
within and without a tube during an experiment was solely 
due to the extra substance required to be tested 3 . 
The prothallia before use were carefully washed in tap- 
water with the aid of a brush. The coverglasses, usually 
12 mm 2 , were supported by the drops of water and the 
prothallia. Strips of paper were thus avoided. Each experi¬ 
ment was repeated with several tubes. A general account 
of the method of use of capillary tubes was given in the 
introduction. For further details reference may be had to 
the papers of Pfeffer. 
In giving the formulae and molecular weights of sub¬ 
stances in the Tables (2nd and 3rd columns) the water of 
crystallization has not been stated. The requisite allowance 
was, however, made when the salts were weighed. The salts 
and other substances tested were dried with the necessary 
caution before use. 
Results. The first three Tables contain a statement of 
1 Voegler, loc. cit., p. 647, also p. 659. 
2 The average of two analyses made in March, 1896, and July, 1894, kindly 
supplied me by Prof. Hofmann of the Institute for Hygiene at Leipzig. The 
water used was practically neutral in reaction to litmus. 
3 The criticism may be offered that in making the solutions with tap-water 
reactions would in some cases take place which might affect the results. This is 
true. If, however, the solutions were made with the distilled water, on diffusing 
out of the tubes reactions would take place with the tap-water outside. I am 
inclined to think that the conditions under which the spermatozoa swim in nature 
