No. 6, DEPARTMENT OF AGRICULTURE. 151 



of the inferior cervical and suprasternal lymphatic glands were en- 

 larged to several times their normal volume and contained numerous 

 areas of caseation. Within the trachea, from the point of inoculation 

 dowu to its bifucatioii and up to the glottis, the mucous membrane 

 lining the ventral half of the tube was thickly studded with oblong 

 red, and evidently young and progressive tubercular growths. These 

 formations were from one-sixth to one-half an inch long, and about 

 iwo-j;hirds as wide; they stood above the surrounding surface from 

 one-twelfth to ooe-half an inch. The postpharyngeal lymphatic 

 glands were enlarged to the size of a hen's egg and loaded with 

 (;aseous material. The lungs contained many grayish nodules one- 

 eighth to one-quarter of an inch in diameter. The smaller were 

 grayish throughout, while the larger had yellow, cheesy centres. 

 These nodules were not set so thickly as in the other control heifer 

 (45071). They averaged from four to five inches a part, and were 

 very evenly distributed throughout both lungs. The mediastinal 

 and bronchial lymphatic glands were enlarged to twice their normal 

 size and contained much caseous material. Many (about eighteen) 

 of the lymphatic glands of the mesentery were enlarged and caseous. 

 No alteration could be found in the mucous membrane or the walls 

 of the intestine. The infection of the mucous membrane of the 

 trachea above the point of inoculation appears to have been due to 

 the carriage upward by coughing of some of the tubercle bacilli 

 at the time of inoculation. It is well known that cattle habitually 

 swallow their expectorations, and this may account for the infection 

 of the postpharyngeal and mesenteric lymphatic glands. 



From the experiments here recorded we believe that we are justi- 

 fied in concluding: 



1. That after repeated intravenous injections of cultures of tuber- 

 cle bacilli from human sputum the resistance of young cattle to viru- 

 lent tubercle bacilli of bovine origin may be increased to such an ex- 

 tent that they are not injured by inoculation with quantities of such 

 cultures that are capable of causing death or extensive infection of 

 cattle not similarly protected. 



2. That by intravenous injection much larger quantities of culture 

 of human sputum tubercle bacilli than are necessary to confer a 

 high degree of resistance, or immunity, upon the vaccinated animal 

 may be administered without danger to that animal. 



We now have in progress incomplete experiments upon a number 

 of young cattle, some of which have been underway since last March, 

 for the purpose of testing the duration of this immunity and the ex- 

 tent to which it is effective in protecting cattle against infection 

 from natural sources. We have also started an experiment which 

 we hope will throw light upon the open question as to the minimum 

 quantities of culture of non-virulent tubercle bacilli that it may be 



