OF MICRO-ORGANISMS. 87 



The manner of conducting the experiment is as 

 follows. A solution of the substance to be experi- 

 mented upon is placed in small capillary tubes with a 

 light-aperture of from five to seven hundredths of a 

 millimeter wide. These capillary tubes dip into a 

 watch-crystal covered with a liquid, wherein quantities 

 of spermatozoids have been placed. Under these cir- 

 cumstances currents of diffusion are soon set up be- 

 tween the tube and the liquid in the watch-crystal, 

 and when the substance experimented upon is the 

 proper one, the spermatozoids are seen to follow the 

 currents of diffusion and to penetrate into the tube. 



The substance exerting such attraction varies 

 with the plants. The author began by experimenting 

 upon the spermatozoids of certain ferns (Adiantum 

 cuneatuni). After a great many fruitless trials, one 

 substance, and one only, proved to be effective: 

 namely, a solution of malic acid or malate. It is to be 

 presumed, then, that, in the organic kingdom, malic 

 acid must be the substance acting as a chemical ex- 

 citation upon the spermatozoids of ferns and guiding 

 them towards the female cellule. 



According to the hypothesis of Pfeffer, the actual 

 process takes place in the following manner. The 

 spore of a fern, falling upon humid ground, germinates 

 and gives birth to a green cordate slip, the prothal- 

 liu/iij upon which are developed the male organs or 

 antheridia, and the female organs or archegonia. At 

 a certain moment, elongate cellules, spirally twisted 

 and extremely mobile, issue from the antheridium: 

 these are the spermatozoids. They are equipped with 

 vibratile cilia, by the help of which they are able to 

 start in search of the female cellule. At the same in- 

 stant, the female organ, the archegonium, opens and 



