86 



MANUAL OF ELEMENTARY ZOOLOGY 



msnt. 



of nucleoplasm by staining. They consist of a kind of 

 matter known as chromatin from the fact that by its 

 affinity for certain dyes it is the cause of the deep staining 

 of the nucleus. 1 Besides these bodies, protoplasm often 

 contains relatively large spaces filled with fluid known as 

 vacuoles. 



Protoplasm is extremely sensitive to the action of ex- 

 ternal agents, from which it is carefully screened 

 protoplasm! ' n the bodies of most animals. Distilled water, 

 solutions of salts, acids, alkalies, and narcotics 

 all have characteristic effects upon it, stimulating, inhibiting, 



or killing it according to their 

 nature and strength. It is also 

 easily stimulated by electric 

 shocks. 



Changes of temperature have 

 marked effects upon it. Moder- 

 ate heat acts as a stimulus, 

 causing increased activity of 

 movements, etc. ; cold has a 

 depressing effect. Heating 

 above about 45° C. kills the 

 protoplasm by causing its pro- 

 teids to set into a solid mass or 

 "coagulate." Cold below 0° C. 

 stops all exhibition of life, but 

 Fig. 45.— A diagram of a trans- un l ess it is extreme does not 

 verse section through the prevent the reappearance of 

 ileum of the frog. vital processes if the tempera- 



c.w., Circular muscle layer ; c./.,eon- ture be raised. 



nective tissue; e6. t epithelium T>„ rt 4. rt „l„„. :„ i_ 



which lines the gut! /.»., longi- Protoplasm is, as we have 

 tudinai muscle layer; mmt., said, the living part of the bodv. 



mesentery ; per. , peritoneum ; T , ■ » ,.1 it j 



rid., longitudinal ridges of ileum. It is here that metabolism goes 



on and all the characteristic 



processes of life take place. The reception ot stimuli, 



conduction, contraction, secretion, reproduction, and so 



forth take place in the protoplasm alone. The rest of 



1 Chromatin consists of various compounds of the class known as 

 nuckins, which contain protein united with another highly complex 

 substance known as nucleic acid, very rich in phosphorus and often 

 in iron. It is probably stored for the use of the nucleus. 



rid. 



