94 PHYSIOLOGY. 



Other without increasing in size. The testes originate in the lower 

 part of the corpora woolfiana, in the embryo, while the kidneys spring 

 from the upper and outer parts. They begin to descend into the scro- 

 tum about the middle of pregnancy ; at the seventh month they reach 

 the inner ring ; in the eighth they enter the passage ; and in the ninth 

 they descend into the scrotum. Sometimes one or both remain in 

 the abdomen, without, however, interfering with their function. 



The sperm is a thick, tenacious, grayish fluid, having a peculiar 

 odour called spermatic^ probably dependent on the secretions mixed 

 with it. It is difficult to analyze it in consequence of its admixture 

 with the secretions of the prostate and Cowper's glands. It is alka- 

 line in its reaction, and contains albumen and a peculiar principle 

 called spertnatin. The so-called spermatozoa are most probably 

 cells of the ciliated epithelium of the mucous membrane lining the 

 genito-urinary apparatus. They are supposed to correspond with 

 the pollen tubes of plants, and are probably the agents by which 

 the fecundating materials of the male are brought into contact with 

 the elements supplied by the female. They seem to be essential to 

 the reproductive process. The sperm also contains seminal gra- 

 nules^ the mode of production of which corresponds with that of 

 other glands. The salts that are found in the sperm are muriates and 

 phosphates, especially the latter. The secretion takes place about 

 the 14th or 15th year and continues till about 60 or 65, and during 

 the whole of this time is much under the influence of the nervous 

 system. 



The spleen^ thymus and thyroid glands^ and supra-renal capsides, 

 are called glandiform ganglia^ sometimes vascular glands. They 

 all act as diverticula to the circulation in their neighbourhood ; the 

 spleen to the portal circulation, the thymus to the lungs in foetal 

 life, the thyroid to the cerebral circulation, and the supra-renal 

 capsules to the kidney. They all seem to share likewise in the pre- 

 paration of the nutritive materials of the blood, assisting in this 

 respect the lymphatic system, to which they seem to be appendages. 



CALORIFICATION 



Is that function by which the heat of organized beings is generated. 

 The source of this heat has long been a disputed question among 

 physiologists. From the fact that plants are capable of generating 

 an amount of heat, sometimes far above that of the surrounding 

 medium, an unequivocal indication is given that we are to look for 

 its source in the organic functions and not in those of animal life. 

 In examining the phenomena in plants which present any relation to 

 this source, we at once perceive that an absorption of oxygen and extri- 

 cation of carbonic acid is continually taking place, (constituting the 

 respiration of plants,) and that these processes occur with great 



