34 INTRODUCTION. 



When it is heated to IGO degrees of Fahrenheit's thermometer, it 

 coagulates like the white of an egg ; but it has no appearance of be- 

 ing organised. 



Red Clot, or Crassamentum, coagulates spontaneously ; and is found 

 to consist of two parts, namely, a fibrous substance called coagulable 

 lymph and resembling very closely the muscular fibres, and a great 

 number of extremely small red globules, which give colour to the 

 blood. 



Secretion. — There are separated from the general mass of blood, 

 by certain organs denominated glands, different kinds of fluids, sub- 

 servient to various purposes ; and the process by which they are 

 formed is termed secretion. 



The glands on the internal coat of the stomach secrete the gastric 

 juice, the liver secretes the bile, and the saliva is derived from the 

 glands of the mouth. In some cases it seems to be a mere filtration 

 or separation of certain substances from the blood : in others it is the 

 formation of a new substance that did not previously exist there. 

 "With regard to the structure of the glands, there is considerable ob- 

 scurity. They consist of a great number of small arteiies which 

 convey the blood to be operated upon, and of corresponding minute 

 veins that return the blood when the operation is complete; but of 

 the intermediate substances or sets of vessels, and of the nature of 

 the action v.hich is going forward in them, we are perfectly ignorant. 



The secretions are exceedingly numerous, very different in their 

 character, and all subservient to some useful purpose. The most 

 important secretion connected with the cow is that of milk, which is 

 formed in that large and complicated gland, the udder, to which so 

 many blood-vessels are directed. 



The functions of the glands are much affected by disease. The 

 secretion is sometimes suspended. In dropping after calving, and in 

 constipation, the secretions of the udder and tlie bowels partially or 

 entirely cease. At other times the fluids which they afford are con- 

 siderably increased. In purging, the glandular follicles of the bowels 

 pour out a great quantity of aqueous fluid. Occasionally the character 

 of the secretion is changed. The discharge of mucus from the nose, 

 under some diseases, and the fluid which escapes from the bowels in 

 dysentery, are very acrid and irritating. 



Perspiration. — A fluid is continually passing off from the surface 

 of the body in the form of an invisible vapour; and when, from exer- 

 cise or other causes, the quantity is increased, it becomes visible like 

 a thick stream, and collects upon the skin and wets the hair, or falls 

 in drops. This is the perspiration or sweat. It is necessary to health 

 that a considerable quantity of fluid should escape in this way. 

 When, from sudden exposure to cold, this discharge from the skin is 

 suppressed, either generally, or in a particular part, rheumatism, or 

 hoose, or catarrh, is the result. Various states of the constitution, 

 and various diseases, will also materially influence the discharge. A 

 cessation of it is by turns the consequence and the cause of disease. 



