20 GENERAL PHYSIOLOGY. 



A third class possess a faculty of drawing to them certain 

 substances contained in the neighboring tissues or fluids, and 

 thus free the organism from which these are detached. In 

 this way the scaly portions of the epiderm, before passing 

 into this condition and foiling off, attract certain calcareous 

 salts, and more especially the phosphates which are con- 

 tained in the organism. This is also an example of the 

 functions of secretion, and these are called secretion globules. 

 These globules, more than any of the others, are characterized 

 by ephemeral existence, and form the largest portion of 

 glands ; the mammary gland is nothing but a membrane of 

 canaliculae, covered with globules which possess at certain 

 times an excessively active life ; then they become very 

 rapidly transformed, and their remains constitute the milk. 



2. The nerve globules (or cells) are not fixed upon sur- 

 faces under the form of membranes, they are hidden in the 

 deeper parts, constituting what has been called the gray 

 nerve-tissue. By direct experiment it is impossible to judge 

 of their life. Yet, like the others, these globules seem to 

 live, and are nourished, and though we cannot judge de visu 

 of their transformations, at least by comparison upon the 

 dead body, these are found differing in appearance and age, 

 some being smaller and transparent, others greater, pale, or 

 filled with granulations, thus indicating a commencement of 

 their decay. Influenced by their metamorphoses, these glob- 

 ules, as well as the nerves with which they enter into commu- 

 nication, are electro-motor. Indeed it is these prolongations 

 or nerve tubes by which the nerve globules are character- 

 ized, and which give them their stellate form. 



3. The blood globules^ whose existence is best known 

 and the most accessible to our senses, form in blood, and 

 consequently in the body about one-twelfth of our whole 

 weight. They differ from the preceding globules in the fact, 

 that instead of having a fixed place they course through the 

 whole organism; their discoid shapes render their transit 

 easier, and during their course they are continually being 

 transformed, certain of them perishing in order to give room 

 to others. During this nomadic state, the blood globule is 

 still characterized by the phenomena of repulsion and attrac- 

 tion, changes of form and composition, loading itself at 

 certain places with chemical products, which seem destined 

 for deposition in other places. 



4. The embryonic cells are so called, because they are the 

 same in the adult that they were in the embryonic stage; 



