April 1, 1891.] 



KNOWLEDGE. 



75 



Style, and on the right for Old Style ; then below this 

 point, and on a line with the given year of the century in 

 tlie centre of the Table, you will find the Dominical 

 Letter for the year. 



TABLE II. 

 For Finding tue Days of the Wekk corrksponding to the 

 Days of the Months; the Dominioai, Letter for the Year 



BEING ascertained BY TABLE L 



Note. — The donhU Ultevs in tich ctnitpfirtmeut refer to hap years, the ^tithjle to 



Directions. — Tlie Dominical Letter answering to the 

 given year being found by Talilc L, find tliis Dominical 

 Letter in the above Table on the same horizontal line 

 with the given month, and under it, in the lower part of 

 the Table, are the days of the week, corresponding with 

 the days of the given month in the same horizontal line 

 on the left-iiand side of the Table. 



EKRATUM. 



In the Article on the Milky Way in the Southern 

 Hemisphere, in the last number of Knowledge, it was by 

 mistake stated that one of the two clusters at tlie bottom 

 of Mr. Barnard's plate of the Sagittarius Region of the 

 Milky Way was entirely wanting in Mr. Russell's photo- 

 graphs. This is not the case, though there is ample 

 evidence of the variation in brightness of many other 

 stars shown upon the plates. Only one of the clusters is 

 shown in the plate from Mr. Russell's photograph ; the 

 other, or preceding cluster, is just outside the field. 



OUR INVISIBLE FOES, OR BACTERIA IN 

 AGRICULTURE. 



By Miss A. W. Buckland. 



Tlli'i first question now asked whenever an epidemic 

 attacks either man or the lower animals is, Is it 

 caused by germs or liacilli floating in the air, or 

 conveyed by water, milk, or any other medium. 

 Tlic germ theory of disease, at present so popular, 

 may be said to have originated in the successiul experi- 

 ments made by M. Pasteur for the cure of the dreadful 



disease known as splenic fever in sheep, and the import- 

 ance of the subject to the agriculturist and merchant, as 

 weU as to the medical profession, may be best understood 

 and appreciated by reference to a few facts. 



During the year 1888 more than eleven hundi-ed head 

 of cattle were slaughtered in Dublin, because they had 

 been in contact with a few suflerLng from pleuro-pneu- 

 monia, whilst the Commission appointed to investigate the 

 best mode of preventing and curing this and simOar 

 diseases, recommended tlie continuous slaughter of all 

 animals which might have been exposed to infection, 

 adding to the report, however, a clause to the effect that, 

 should experiments in inoculation be deemed advisable, 

 such experiments should be carried out only with the 

 most stringent precautions. 



Meanwhile the Government of India, as the result of 

 experiments made, has ordered the inoculation of all the 

 valuable elephants in the Government stables, for the 

 prevention of a disease by which they have hitherto been 

 decimated. M. Pasteur, as is well known, proi)osed to 

 exterminate the millions of rabbits which have become 

 such a pest in Australia and New Zealand, by introducing 

 among them by inoculation the disease known as chicken- 

 cholera, deadly to fowls and rabbits, but harmless to other 

 animals and to man. But although the Australasian 

 Governments approached the matter in a scientific spirit, 

 and gave every facility for properly conducted experiments, 

 under the supervision of Dr. Katz, bacteriologist, employed 

 by the Linnean Society, — (1) to test the commuuical)iUty 

 of chicken-cholera to rabbits, the possibility of spreading 

 the disease from rabbit to rabbit, and the readiness and 

 channels by which such commimication could be procured ; 

 (2) to ascertain whether the disease is transmissible fi'om 

 infected rabbits to other domestic animals — mammals and 

 birds ; (3) to ascertain whether the infectivity of the 

 disease is weakened by repeated transmissions from rabbit 

 to rabbit, — the experiments do not api^ear to have been 

 successful, for although the rabbits inoculated die, they do 

 not apparently convey the disease to others. Nevertheless 

 it seems to be demonstrated beyond dispute, that certain 

 forms of bacteria invariably accompany certain diseases, 

 and reproduce similar diseases when introduced by inocu- 

 lation into the bodies of men or animals. 



These iiiicro-oiytniisms, so exceedingly small as to be 

 absolutely invisible to the naked eye, have yet been so 

 carefully observed microscopically, and so faithfully re- 

 produced and enlarged by photography, that they can be 

 studied in all their wonderfully varied forms ; and the 

 difl'erences between them are sufficiently marked to be 

 appreciated even by the non-scientific observer. Some 

 resemble dots in various groups ; some are twisted spirals ; 

 some look like chains ; others resemble small bags, with 

 strings attached ; some look like branches of trees, whUst 

 others are simply rods crossing each other. 



If we regard them as animals, they do not appear to 

 possess any bodily parts, neither head nor tad, neither 

 heart nor stomach ; whilst if they are vegetables, they 

 have neither roots nor branches, although abounding in 

 spores. That they are very much alive cannot be doubted, 

 nor the fact that they multiply with the most astonishing 

 rapidity. The growth of one which occurs in sugar is so 

 rapid that 49 hectolitres of molasses were converted into 

 a gelatinous mass in twelve hours. 



Micro-organisms can be cultivated in various media, 

 and wUl still retain their identity, but they cannot all be 

 cultivated in the same media. . Dr. C'lookshauk says : 

 •' Some species cannot be cultivated artificially, others wUl 

 only grow upon blood- serum ; many grow upon nutrient 

 gelatine, but some species only if it be acid or alkaline 



