34 • TRANSACTIONS OF THE ILLINOIS 



four to eight individuals. They are only sTsm-s of an inch in diame- 

 ter. — so excessively minute that it would take more than eight 

 millions of them to cover the head of an ordinary pin, while the ex- 

 treme tip of an average point of such a pin would give room for more 

 than eighty thousand of them to lie side by side. These have been 

 described by Cohn under the name of Micrococcus homhtjcis, and are 

 the characteristic bacterium of this disease. At first the most care- 

 ful search will not discover them in the blood; but usually, before 

 death, they seem to penetrate the intestinal wall and swarm in all 

 the fluids of the body. That the disease they characterize is conta- 

 gious was shown by Pasteur by numerous experiments like the fol- 

 lowing: 



On the 20th of May he selected three identical lots of perfectly 

 healthy worms, twenty-five in each lot, which had nearly got their 

 growth. One of these he set aside as a check lot, and gave it the 

 usual treatment of the silk-worm. The food of the second twenty- 

 five was sprinkled with dry dust from a silk-worm hatchery which 

 had been occupied the previous year by worms sick with flacherie. 

 The food of the third lot was treated with the same dust suspended 

 in water and sprinkled upon it. The check lot went through their 

 transformations without accident, all in perfect condition. Of the 

 second lot, the food of which was powdered with infected dust, two 

 worms died of flacherie on the 21st, two on the 22d, three on the 24th, 

 one on the 25tli, one on the 28th, one on the 31st, and thirteen of 

 the worms transformed into chrysalids, one of which was diseased. 

 From the third lot, three dead worms were removed on the 21st, 

 three on the 22d, two on the 23d, one on the 24th, three on the 25th, 

 two on the 26th, and two, evidently seriously diseased, were removed 

 on the 29th. Another worm died on this day, and only seven chrysa- 

 lids were finally produced. This experiment showed clearly that dust 

 from an infected hatchery, which had been unoccupied for a year, 

 still contained the virus of the disease in an active state. Again, on 

 the 23d of May, the food of twenty healthy worms was brushed with 

 the contents of the intestinal canal of a silk-worm at the point of 

 death with flacherie. Six days after one worm was dead; on the next 

 day another. On the 1st of June one died, on the 4th two. on the 5th 

 another, and on the 7th two more. Twelve cocoons, two of them 

 diseased, resulted from these twenty worms. On the 22d of May 

 twenty-five perfectly healthy worms were similarly infected with 

 water in which a fragment of a worm dead from flacherie had been 

 macerated for a short time. The worms ate, without reluctance, the 

 leaves upon which this fluid had been brushed. On the evening of 

 the next day two of them were dead; on the morning of the 24th 

 two more, and in the afternoon another. Two died on the 25th, one 

 on the 28th, and four on the 30th. On the 1st of June one died, on 

 the 3d another, on the 7th still another. Nine finally transformed 

 into chrysalids: but in five of these nine, bacteria were found, indi- 



