320 GENERAL ANATOMY. 



sels to the excretory ducts, and vice versa; and the difficulty 

 encountered in obtaining the same results in the lobulated and 

 granulated glands. 



However this may be, the texture of the glands seems very 

 positively to result from the intimate association of ramified 

 excretory ducts, closed at their origin, with blood-vessels, 

 lymphatics and nerves, situated in their intervals, dividing 

 and terminating in their thickness; the whole being united by 

 cellular tissue and enveloped in membranes. 



488. The function of the glands consists in a mode of secre- 

 tion which is called glandular. All secretions generally con- 

 sist in the formation of a particular humour, of which the 

 blood furnishes the materials. Glandular secretion only dif- 

 fers from $e others, (the follicular and perspiratory secre- 

 tions,) by the greater complication of its organs. 



With a single exception, the same blood, arterial blood only, 

 is sent into all the glands ; the number, the size, the direction, 

 the mode of distribution of the vessels, and the degree of 

 tenuity which they reach by their successive divisions, can 

 only have an influence on the quantity of blood which arrives 

 in the gland, and on the rapidity of its course. However, a 

 part of the blood being brought back by the veins, and another 

 liquid by the lymphatics, the glands pour forth through their 

 excretory ducts, humours as different from each other, as the 

 saliva, the tears, the bile, the urine, the sperm and the milk. 



What are then the nature and cause of the conversion of the 

 blood into secreted humours? It has been thought that the 

 change and its cause were purely mechanical, and depend on 

 the size and shape of the openings through which the humours 

 issue from the vessels; it has been supposed with more proba- 

 bility, that it was owing to a chemical change, that is to say, 

 another elementary composition; but this change occurs only 

 in organized bodies, and in some of their organs. This differ- 

 ence is then owing to modifications of their substance, in the 

 same manner as we see different vegetables planted in the 

 same soil, and surrounded by the same atmosphere, produce, 

 some gum, others an acid, others resin, &c. Glandular se- 

 cretion, like the others, is then a function of the living and 



