188 MICHIGAN ACADEMY OF SCIENCE. 



1900, of the one hundred reported outbreaks, fifty-one per cent were re- 

 stricted to the one house where the first case occurred. The final data 

 for 1901 is not yet avaihible, but from evidences at hand the indications 

 are that the per cent of outbreaks restricted to the one house where the 

 first case occurred will be at least sixty per cent; thus proving that the 

 continual urging of local boards of health to publicly recommend general 

 vaccination and revaccination of all persons not successfully vaccinated 

 within the last five years, and the offering of free vaccination to all who 

 are not able to pay for the same; the isolation of all sick and infected 

 persons so long as there is danger of their communicating the disease, and 

 the vaccination or isolation of all jjersons exposed to smallpox, has been 

 the cause of much good resulting therefrom. 



THE AERATION OF MILK. 



C, E. MARSHALL. 



Perhaps no question connected with the production of milk for city 

 consumption and for the manufacture of butter and cheese has caused 

 so much agitation as aeration. It may be assigned largely to the fact 

 that aeration has had attributed to it a pregnancy of possibilities formu- 

 lated upon mere conjectures. Many assumptions have therefore followed 

 and the conclusion, that aeration is an essential factor in the production 

 of pure milk, has taken its place coordinately with cooling. This associa- 

 tion has been emphasized by the manufacture of combined aerators 

 and coolers. It has been recognized for many years that the animal 

 odors and taints are removed to a greater or less degree by the methods 

 of aeration now in vogue ; beyond that, nothing can be considered as 

 actually demonstrated, notwithstanding the work of several practical 

 dairymen to determine that it has a direct bearing upon many practical 

 dairy operations. The cooling of milk has been shown to be exceedingly 

 valuable bacteriologically and is thoroughly understood in this aspect, 

 still so intimately have aerating and cooling been connected that we at- 

 tribute to aeration what really belongs to the cooling and fail to disas- 

 sociate them into their individual capacities. Perhaps we can safely 

 assume from practical experience if milk becomes tainted in any 

 way either through the agency of food for the animal or through the 

 bacterial growth in the milk that the resulting taint is removed in a 

 perceptible degree and partially overcome for a time; if it is due to 

 bacterial growth the taint will return in time, unless aeration checks the 

 germs concerned, but if it is due 1o the food it may be permanently lessen- 

 ed. It should not be forgotten that by the lowering of the temperature 

 the odors and taints are reduced so far as the sense of smell can detect 

 but upon heating they return. 



Arnold as early as 1871 made these statements: "Because the cowy 

 smell has died away when the milk is cooled down to 70° or below, it has 

 usually been supposed that the odor or cause of the odor was wholly 

 removed. But it is by no means necessarily so; for, unless the cooling 

 has been very slow, or the milk has been spread so thin as to make the 



