1000 THE PHYSIOLOGY OF REPRODUCTION. 



the spermatozoa in greater abundance than in any other protein. 

 The protamins differ from most other protein compounds by their 

 relative simpUcity; they contain no cystin grouping, therefore no 

 sulphur; no carbohydrate grouping in most of the compounds 

 examined; and no tyrosin complex. In the spermatozoa of some 

 fishes the protamins are replaced by more complex compounds 

 belonging to the group of histons which show properties somewhat 

 intermediate between those of protamins and ordinary proteins, 

 and in general it may be said that the head of the spermatozoon, 

 like the nuclei of cells in general, consists chiefly of a nucleoprotein 

 compound, that is, a compound of nucleic acid with a protein body 

 of a more or less distinctly basic character.* The nucleic acid com- 

 ponent of the spermatozoon resembles the same substance as 

 obtained from the nuclei of other cells. In the spermatozoa of the 

 salmon this nucleic acid has the formula C^pHsgNi^PPog- On 

 decomposition by hydrolysis it yields at first some of the purin bases 

 (adenin, guanin), and on deeper cleavage a number of compounds, 

 including the pyrimidin derivatives, thymin, uracil, and cytosin. 

 While the chemical studies upon spermatozoa, thus briefly referred 

 to, have greatly extended our knowledge, it is still impossible to 

 say that they have given any information concerning the peculiar 

 functions of the spermatozoa in fertilization. 



The Act of Erection. — In the sexual life of the male the act of 

 erection of the penis during coitus offers a most striking physical 

 phenomenon. During this act the penis becomes hard and erect, 

 owing to an engorgement with blood. The structure of the corpora 

 cavernosa and corpus spongiosum is adapted to this function, being 

 composed of relatively large spaces inclosed in trabeculse of connec- 

 tive and plain muscle tissue, — the so-called erectile tissue. Many 

 theories have been proposed to explain the mechanism of erection, 

 but it is generally agreed that the work of Eckhard f demonstrated 

 the essential facts in the process. This investigator discovered that 

 in the dog stimulation of the nervi erigentes causes erection. These 

 nerves are composed of autonomic fibers arising from the sacral por- 

 tion of the spinal cord (see Figs. Ill and 112). They arise from the 

 sacral spinal nerves, first to third (dog), on each side and help to 

 form the pelvic plexus. They contain vasodilator fibers to the penis, 

 as well as to the rectum and anus, and also visceromotor fibers to the 

 descending colon, rectum, and anus. Eckhard, Loven, and others J 

 have shown that when these fibers are stimulated there is a large 

 dilatation of the arterioles in the erectile tissue of the penis and a 



* Burian, loc. cit. 



t Eckhard, "Beitrage zur Anatomie und Physiologie," 2, 123, 1863, and 

 4, 69, 1869. 



X See especially Fran^ois-Franck, "Archives de Physiol, norm, et pathol.," 

 1895, 122, 138. 



