SIMPLE OR HOMOGENOUS FLUIDS. 65 



in mammals they are free from their departure from the ovary 

 until their attachment to the uterus, and even afterward they 

 are in a sense independent. 



The cellular fluids of the body are the blood, lymph, and 

 semen. They consist of actively vital cells free in a fluid 

 matrix. They can be regarded as liquid tissues analogous in 

 all respects to the solid tissues, being composed of cells and 

 an abundant intercellular substance, which in this case is fluid. 

 The latter differs from the matrix of the solid tissues, how- 

 ever, in that it is not produced by the vital activities of the 

 cells suspended in it. 



The blood consists of cells or corpuscles of three kinds, red 

 corpuscles, white corpuscles or leukocytes (of which there are 

 several varieties), and blood-plates. 



Lymph consists of a fluid portion, or serum, containing 

 lymph-corpuscles, which are similar to or identical with some 

 forms of leukocytes. Leukocytes and lymph-corpuscles often 

 find their way into the fixed tissues or on mucous surfaces. 



Semen is a thick opaque fluid containing large numbers of 

 spermatozoa, together with some loosened cells and granules. 



The simple or homogeneous fluids are mainly the secretions of 

 the various glands, consisting usually of clear, transparent solu- 

 tions without any proper cellular or formed elements. Under 

 the microscope they exhibit no structural features, and the 

 study of their composition is a matter for chemical or micro- 

 chemical methods. Among them may be mentioned the urine, 

 perspiration, saliva, bile, gastric juice, etc. ; also the fluids 

 moistening the mucous surfaces, of which mucus is a promi- 

 nent constituent. 



Although these fluids contain no cellular elements as proper 

 or essential ingredients, yet they sometimes, notably the saliva 

 and urine, contain a few adventitious cells derived from the 

 mucous membrane lining the surface of the cavities where 

 they occur. The chief cells thus found are leukocytes or 

 lymph-cells (as the "salivary corpuscles") which have worked 

 their way through the mucous membrane to the surface ; also 

 ordinary epithelium-cells cast off from the epithelial covering ; 

 and "mucous corpuscles," or " mueocytes," young germinal 

 epithelium-cells from the lower epithelial layers (especially in 

 the bladder) which have grown rapidly and been thrown off 



5 Hist. 



