COMPOUND ANIMAL SUBSTANCES. 91 



>\ater, the substances wliich are inclosed by the fibrin gradually 

 separate themselves from it, as for instance albumen, blood- 

 corpuscles, &c., and the fibrin remains devoid of colour, very 

 small in proportion to the clot from which it has been obtained, 

 and forming a membranous, stringy, or flocculent mass. 



If the fluid has an acid reaction, the flocculi may arise from 

 coagulated casein, or caseous substances. In this case dis- 

 tilled water has no effect on them. The existence of casein 

 in milk is universaDy known. Other fluids which contain 

 caseous principles, as for instance, mucus and saliva, usually 

 maintain an alkaline reaction for a considerable period, and 

 thus hold the casein in solution. Pus has usually a neutral 

 reaction, occasionally however pus from the lungs is acid. 



If the flocculi are observed to be floating on the surface of 

 the fluid, if they exhibit a frothy appearance, or seem more or 

 less globidar, are of a whitish or yellow colom', and possessed 

 of little tenacity, they are composed of mucus, and the micro- 

 scope will reveal the presence of mucus-granules. A tenacious 

 substance of a yellow or brownish colom', and not unfrequently 

 containing blood, is occasionally foimd to be deposited in cer- 

 tain animal fluids, for instance, in the urine diu'ing phthisis 

 vesicce. It is possessed of more elasticity than mucus, and is 

 verj^ probably composed partially of fibrin^ although it is usually 

 regarded as pus. 



2. If vdih the aid of the microscope we can detect blood- 

 corpuscles in the fluid, we may infer the presence of globuHn 

 and hsematin. We recognize the blood-corpuscles, and dis- 

 tinguish them from other objects by their discoid form, and 

 their yellow coloui'. When blood is mixed with a serous or 

 watery fluid, it frequently happens that the discoid form is no 

 longer appai'ent ; if however a solution of common salt, or of 

 muriate of ammonia be added to a portion of the fluid, the 

 characteristic shape of the blood-corpuscles will be again ren- 

 dered perceptible. Fluids in which blood-corpuscles are found, 

 are always of a reddish tinge, and invariably contain albumen. 



3. The microscope further enables us to detect the follow- 

 ing sohd forms in flmds : a, fat-vesicles ; b, chyle-corpuscles ; 

 c, mucus-corpuscles ; d, pus-corpuscles ; e, epithelium-cells ; 

 /, saliva-corpuscles ; g, various crystalline forms of salts, uric 

 acid, cholesterin, &c. 



