Minute Organisms. 109 



Human Subject by Consumption of Milk from Cows having Foot- 

 and-Moutb Disease," and his conclusions are that " a disease ap- 

 pears sometimes to have been produced in the human subject when 

 the milk of cows suffering from the disease has been Ireely used 

 without being boiled;" but he adds, " in a very large number of 

 cases the milk of cows undoubtedly affected has been used without 

 producing any noticeable marked effects." This seems to be analo- 

 gous to the well-known fact that persons or animals exposed to 

 contagion do not always catcli the diseases which those contagions 

 are supposed competent to produce ; and this suggests the important 

 inquiry as to what conditions the contagions require for their mis- 

 chievous activity, and also whether micro2yTne3, which under some 

 circumstances produce disease by their processes of growth or de- 

 velopment, can develop under other conditions without inducing 

 such results. In the case of cow's milk infected with germs of 

 foot-and-mouth disease, Londoners have been supposed to have 

 derived advantage fi'om the well-known practice of the trade to 

 distribute their article in the mild form of milk and water ; but the 

 addition of the aqueous fluid is not always contributive to our 

 safety, and Dr. Ballard has recently published a pamphlet detailing 

 a series of cautious researches, which render it probable that a fatal 

 outbreak of typhoid fever in Ishngton may have originated through 

 the milk of a particular estabhshment being mixed with water from 

 an underground tank, which by the work of rats had been made to 

 communicate with some old drains. Unfortunately, no microscopic 

 examination of the water fi'om this tank was made at the time of 

 the fever, as its existence was not then known, and at a later date 

 Dr. Bernays stated that its analysis coincided with that of the New 

 Kiver Company supply. 



That air conveys with its cui'rents to various places germs, 

 spores, and particles of different substances, has been long known ; 

 but the general public has been led to take much interest in the 

 matter, and perhaps to entertain exaggerated views of danger, 

 through Professor Tyndall's lectures and exhibition by the electric 

 hght of the particles which constitute the motes in the sunbeams, 

 and which have been gazed at for generations. Some very interest- 

 ing researches on the jiarticles floating in air will be found in 

 Pouchet's ' Heterogenic,' published in 1859, under the head of 

 " Micrographie Atmospherique," in which he shows that the greater 

 portion of these particles consists of small fragments of various 

 materials exposed to friction and disintegi-ation, and by no means 

 comprises the quantity of eggs, spores, &c., that some have imagined. 

 In other investigations it was found that the air of rural districts 

 contained, as might be expected, fewer particles than that of towns, 

 and mountain regions were almost free from them. 



Dr. Maddox brought this question before us in a paper which 



