DISEASES OF THE URINARY AND GENERATIVE ORGANS. 21 5 



done with is certainly remarkable: according to the amount of 

 pressure in the blood stream, which is, in a great measure at least, 

 regulated by the force of the heart's contractions, so chiefly is the 

 secretion of the urine augmented or decreased; at the same time 

 the secretion may be modified if there is an obstruction in the 

 veins, which is one way of explaining in what way the liver, 

 when the portal circulation is out of order, has an influence on 

 the urinary secretion; by way of illustrating the power which 

 blood pressure has in the production of urine, it is only necessary 

 to refer to the well known fact that in hot weather much less urine 

 is passed than in cold, assuming that the amounts of fluid taken 

 into the body are nearly equal; this is due to the relaxed condition 

 of the capillaries of the skin through which the watery constitu- 

 ents of the blood exude in the form of perspiration, consequently 

 the amount of fluid that has to be filtered through the kidneys is 

 much reduced. 



It should also be understood that while one of the main func- 

 tions of the kidneys is that of filtration from the blood, there are 

 recognized constituents in the urine which have not been observed 

 in the same form in the blood, hence the conclusion has been ar- 

 rived at that the kidneys have the power of secretion, and that 

 certain constituents are added to the urine in its passage 

 through the tubes of the kidneys; putting these facts together, it 

 will be seen that the functions ot the kidnej-s are of a twofold 

 character; namel}^ first, the function of filtrating the watery and 

 soluble substances from the blood; and, second, the removal of 

 certain constituents w4iich go to make up the whole of the urine 

 bj' means of a secretory power possessed by the uriniferous tubes; 

 these facts are worth noting and have a special interest when deal- 

 ing with a case of suppres.sion of urine in the horse. If a kidney 

 be cut into two equal sections and the surface of the cut portion 

 examined under a powerful magnifying glass, it will be seen that 

 it consists mainly of convoluted tubes of various sizes, while the 

 central portion of the organ forms a cavit}' w^herein the secretion is 

 collected; from thence the urine passes down a single tube of pro- 

 portionately larger calibre and is emptied into the bladder, w'hich 

 is an organ consisting of various kinds of muscles lined internally 

 with mucous membrane; as the bladder becomes filled the desire 

 to evacuate same arises throu2:h the influence of certain nerve 



