368 KANSAS CITY REVIEW OF SCIENCE. 



cut meat is frequently exposed for sale in our markets, where flies abound. Con- 

 sidering the habits and habitats of the house-fly, it will appear evident that should 

 it prove to be a carrier of poisonous bodies, its powers to distribute them, in hu- 

 man habitations is greater than that of any other known insect. Under our sys- 

 tem of public travel, the common house-fly may be transported from one end of 

 the continent to the other. It may feast to-day in the markets of Washington, and 

 to-morrow in those of New York, and in a like manner -it may be transported 

 from a hospital for contagious or infectious diseases to homes in the vicinity, or 

 even in remote localities. It may also be taken from one hospital to another, or 

 '"rom one ward to another within the same hospital, and may plant the germs of 

 disease in exposed wounds, or deposit them in food, or liberate them in the at- 

 mosphere breathed by patients affected by diseases of a different class. 



Many of the germs of putrefaction — spherical bacteria, for example — are in 

 dividually not larger than one forty-thousandth part of an inch in diameter, and 

 over 30, 000, 000 of these in a state of aggregation could pass through the eye of the 

 finest needle ; and owing to their minuteness, millions of such germs could easily 

 be carried to a distant city by a single fly. We should take into consideration also 

 the rapidity with which such forms of bacteria multiply. A bacterium which 

 will reproduce by fission (the one dividing into two) in one hour may in twenty- 

 four hours have a posterity of 33,000,000, for a geometrical progression of twen- 

 ty-four terms, with one for its first term and two for its common ratio, has 33,- 

 554,432 for its twenty-fourth term. 



To test practically the question whether flies may become the carriers of 

 contagious germs, I instituted a series of experiments. In a glass receiver having 

 a capacity of about five gallons of air, I placed several hundred house flies which 

 had been caught in an ordinary fly-trap. Within the receiver was placed a quanti- 

 ty of the spores of the red rust of grasses, (tricholoma rubra-vera). The flies at 

 first did not seem to esteem the spores as suitable food, but on the morning of 

 the third day I found that the rust was replaced by larvae and remains of eggs of 

 the common house-fly. 



The eggs were deposited and hatched between Saturday noon and the fol- 

 lowing Monday morning, 9 o'clock, or in about forty-eight hours On the fol- 

 lowing day I placed in the receiver about a quarter of an ounce of the same de- 

 scription of spores combined with sugar. The flies partook of this confection, 

 consuming the sugar and most of the spores. In about twenty-four hours after 

 the flies had partaken of this mixture I killed and dissected a number of them, 

 and found the small intestines intensely colored, of a deep reddish orange shade, 

 representing the digested spores of tricholoma. I observed in the contents a few 

 well-defined orange spores, but none of them appeared to have germinated. 



Fastened between the hairs on the limbs of each of the flies examined I 

 found a number of the spores, and the efforts of the fly to get rid of them only re- 

 sulted m attaching them more firrlily to it. They might, however, be brushed 

 off by objects with which they were brought in contact, while their germinating 

 powers would long outlast the Hfe of the insect itself. It was evident from this 



