THE WONDERS OF LIFE 



bacteria win the battle, they are transported into 

 other parts of the body by the leucocytes; they dis- 

 tinguish their plasm by taste, and may cause a deadly 

 infection. 



We have a particularly interesting and important 

 species of chemical irritation in the mutual attraction of 

 the two sex-cells, to which I gave the name of chemo- 

 tropism thirty years ago, and which I described as the 

 earliest phylogenetic source of sexual love (see the 

 Anthropogeny, chapters vii. and xxix.). The remarkable 

 phenomena of impregnation, the most important of all 

 the processes of sexual generation, consist in the coales- 

 cence of the female ovum and the male sperm-cell. 

 This could not take place if the two cells had not a 

 sensation of their respective chemical constitution and 

 disposition for union; they come together under this 

 impulse. This sexual affinity is found at the lowest 

 stages of plant life, in the protophyta and algae. With 

 these both cells — the smaller male microgameta and the 

 larger female macrogameta — are often mobile, and swim 

 about in order to effect a union. In the higher plants 

 and animals only the small male cell is mobile as a rule, 

 and swims towards the large immobile ovum in order to 

 blend with it. The sensation that impels it is of a 

 chemical nature, allied to taste and smell. This has 

 been proved by the splendid experiments of Pfeffer, who 

 showed that the male ciliated cells of ferns are attracted 

 by malic acid, and those of the mosses by cane-sugar, 

 just in the same way as by the exhalation from the 

 female ovum. Conception depends on exactly the same 

 erotic chemotropism in the fertilization of all the higher 

 oiTganisms. 



Erotic chemotropism must be regarded as a general 

 sense-function of the sexual cells in all amphigonous 

 organisms, but in the higher organisms special forms 

 of the sex -sense, connected with specific organs, are 



306 



