240 THE MICROSCOPICAL NEWS. 
less of these conditions is required than in Southern Texas, and in 
Southern Texas much less than in Northern Texas or in the Indian 
Territory. What these conditions consist in is not, or at least, but 
partially, known. Difference in climate and temperature seems to 
be of some influence, but of hardly enough to afford an explanation. 
Some classes of bacteria, as is well known, after a certain length of 
time, or after having reached a certain stage of development, 
exhaust (sterilize) their medium, or the subject they live in, and all 
propagation ceases till they are transposed to a new, fresh medium. 
Some species even make a further propagation in the same medium 
impossible by their own products. So it may happen that in 
certain infectious diseases, the first attack produces more or less 
immunity against further attacks. In most bacteritic diseases, how- 
ever, in swine-plague for instance, this immunity is only partial, and 
not lasting. I have observed that one and the same hog—not- 
withstanding that a hog under domestication is for obvious reasons 
only a short-lived animal—suffered three times from swine-plague, 
and cases in which an animal was attacked a second time are quite 
numerous. Such cases undoubtedly would be still more frequent 
if the disease (the first attack) were not so fatal as it generally is. 
In regard to southern or Texas cattle fever, too, the immunity en- 
joyed by southern cattle, while on their native range, is invariably 
destroyed if these cattle are taken north, and kept there over 
winter. Consequently, M. Pasteur’s inoculation theories need not 
to be tried on so-called Texas cattle fever. 
(Zo be continued.) 
OUR BOOK-SHELF. 
THE CHEMISTRY OF Foops, by James Bell, Ph.D., Principal of 
the Somerset House Laboratory. Pt. I, 120 pp. Tea, Coffee, 
Cocoa, Sugar, &c. Pt. II., Milk, Butter, Cheese, Cereal foods, &c. 
London: Chapman and Hall. 
The South Kensington Museum has done much good in its time 
by the dissemination of useful information of various kinds, but 
the publication of a series of Science Handbooks is one very good 
means of educating those living at a distance from the great 
Metropolis, which has not generally been attempted before. 
Mr. James Bell, in his preface to this work, tells us that it “is 
intended partly as an aid to those who may desire to carefully 
examine the illustrations of Food adulteration in the Bethnal Green 
branch of the South Kensington Museum, and partly as a contri- 
