60 DEPARTMENT OF AGRICULTURE. 



for the first time directed to the disease in cattle. It is conditioned by the peculiar 

 anatomical arrangement of the lungs of these animals, in which the lobules are separated 

 from each other, by processes of the pleura or by septa of loose connective tissue, to an 

 extent which has no parallel in the human subject. The inflammation of the pleura 

 speedily extends to these loose interlobular septa, in which a rapid lymph formation takes 

 place, resulting in the production of the thick yellowish layers above described. Very 

 often these thickened septa are softened in their central portions, where they frequently 

 present irregular cavities containing a turbid serum or a puriform fluid, while the lymph 

 next the surfaces of the adjacent lobules is much denser and more consistent. 



Amidst these extensive changes of the lung tissue, the larger air passages usually 

 remain singularly free from disease. Those which actually ramify in the diseased portions 

 of the lung present more or less congestion of their mucous membrane and generally con 

 tain a variable quantity of puruloid mucus, or of yellow lymph, not unlike that seen in the 

 pleural cavity ; but the bronchial inflammation which exists in these situations does not 

 generally extend to the other bronchial tubes or the tracliea. 



In considering the general character of the lesions briefly sketched in the foregoing 

 paragraphs, it appeared to me that the following points were especially deserving of micro 

 scopical investigation : the alterations in the lung parenchyma ; those in the connective 

 tissue of the pleura, pericardium, and interlobular septa ; the structure of the lymph 

 masses adherent to the pleura and pericardium, and the peculiar transformation of portions 

 of the adipose tissue in the vicinity of the heart. 



For the purposes of this investigation I not merely examined the elements obtained 

 by tearing and scraping the tissues to be studied, and observed fragments or sections 

 immersed simply in the serum which drained from the cedernatous organ, but I made use 

 of the well-known glycerine method, and, above all, caused my assistant, Dr. Schaeffer, to 

 prepare the thin section to which I have already alluded. For this purpose, the process 

 most generally employed at the museum for the preparation of thin sections of pathologica 

 tissues was resorted to, a process which I have described in full elsewhere.* Its general 

 features are as follows : 



Small portions of the parts intended for investigation are hardened and gradually 

 robbed of their moisture by soaking them for a few days in alcohol of moderate strength, 

 replacing this by alcohol of 95 per cent., in which they remain a few days longer, when 

 they are immersed in absolute alcohol until they are hard enough to cut into thin sec 

 tions by means of a razor and one of the ordinary cutting machines. The nuclei are then 

 stained with Thiersch s carmine fluid, or with carmine dissolved in a saturated solution of 

 borax, after which they are again placed a few days in absolute alcohol, and finally 

 mounted in a solution of Canada balsam in chloroform or benzole. When the solution of 

 carmine and borax was -employed the sections were subsequently treated with oxalic acid, 

 to give brilliancy to the carmine staining. 



Instead of the above, some of the sections after staining were immersed for some 

 time in glycerine and finally mounted in a jelly of glycerine and gum arabic. These prep 

 arations were at first quite as beautiful as those mounted in Canada balsam, but, though less 



* American Journal of Medical Sciences, Januury, 1869, page 277 ; see, also, Instructions to Medical Officers to -whom 

 a Microscope is furnished, Surgeon General s Office, July 1, 1868. 



