616 A MANUAL OF BACTERIOLOGY 



minutes, and that the infective properties of tuberculous sputum, 

 tested on guinea-pigs, were destroyed by a temperature of 65 C. 

 acting for fifteen minutes in five out of six instances. Woodhead s 

 experiments (First Royal Commission on Tuberculosis) gave irregular 

 results which seem to be explained by Theobald Smith's careful 

 work. 1 This showed that tuberculous milk was rendered non- 

 infective by heating to 60 C. for ten to fifteen minutes, provided 

 there was no formation of a surface scum ; the latter seems to protect 

 the bacilli. Russell and Hastings 2 confirmed Smith's experiments, 

 and assert that it is sufficient to heat milk to 60 C. (140 F.) in 

 a closed receptacle for a period of not less than twenty minutes in 

 order to destroy the tubercle bacillus. The surface scum forms 

 on milk only when it is heated in contact with air ; all pasteurisers, 

 therefore, should be closed vessels. The writer has devised a 

 simple form of domestic pasteuriser, which is made by Messrs. 

 Allen and Hanbury. 



The occurrence of so-called leucocytes and pus-cells in 

 milk must be considered. A certain number of cells 

 resembling polymorphonuclear leucocytes are always 

 present in milk, more numerous during the first week of 

 lactation and then accompanied by colostrum corpuscles. 

 An excess of these cells may indicate some local inflamma- 

 tory affection of the udder, or, if streptococci and blood 

 are present in addition, suppuration, but not necessarily, 

 for Russell and Hoffman, and Revis have shown that a 

 very large cell count (500,000-1,000,000, or even 10,000,000, 

 per c.c.) may often be obtained from quite healthy cows. 

 The nature of these cells has been the subject of an extended 

 investigation by Hewlett, Villar, and Revis. 3 Their con- 

 clusion is that the majority of these cells are not leucocytes, 

 but are germinal cells of the secreting epithelium of the 

 udder. Blood may also be present transitorily in health 

 (Revis). The presence of squamous epithelial cells indi- 

 cates desquamation from the teat or udder or from the 

 hand of the milker i.e. want of cleanliness. 



1 Journ. Exper. Med., vol. iv, 1899, p. 217. 



2 17 ih Ann. Rep. Wisconsin Agricult. Exp. Station. 



3 Journ. of Hygiene, vols. ix, x, xi, and xiii. 



