At the suggestion of Professor Dumas, the Government induced Pasteur to examine into the "disease." He had seen in a report on the epidemic made by M. de Quatrefages, that there were found in the diseased worms certain minute corpuscles only to be seen under the microscope. When in June, 1865, Pasteur arrived in the town of Alais, he found these corpuscles without difficulty. He traced them from the worm to the chrysalid, in the cocoon, and thence to the moth; he found worms hatched from the eggs laid by these moths invariably developed the corpuscles. He crushed a corpuscular moth in water, painted a mulberry leaf with it, fed it to a healthy worm, and the corpuscles developed. He hatched eggs from moths free from corpuscles and secured healthy worms. While working on the "disease," Pasteur discovered in 1867 that the mortality among the worms was in part due to another disease, the flacherie, and this he found was the result of imperfect digestion.
Pasteur in his Laboratory.
Flacherie was contagious, and was caused by the fermentation of the food eaten in the body of the worm. The causes of this fermentation, the condition of the leaves, the temperature, and others were pointed out. As the result of five years' work, Pasteur had restored the silk industry to its former position, and had shown that the microscopic examination of the moth laying the eggs to be hatched was a perfect safeguard against pebrine and flacherie.
At the request of the emperor, Pasteur went to the Villa Vicentia, in Austria, belonging to the prince imperial. For ten years the silk harvest there had not paid the cost of the eggs.
Although he was just recovering from an attack of paralysis brought on by overwork, Pasteur travelled to Austria, introduced his methods and the sale of the cocoons gave the villa a net profit of 26,000,000 francs. No wonder it was said of him that his discoveries alone exceeded in money value to the French people the war indemnity paid by them to the Germans.
Splenic fever, called charbon in France, had for years decimated the flocks in France, Italy, Russia, Egypt, Hungary, and Brazil. It attacked the horse and cow as well as the sheep, and human beings died of it when they developed malignant pustule. Many scientific men had studied it, but Dr. Davaine, in 1850, was the first to find in the blood of a sheep that had died of the disease, "little thread-like bodies about twice the length of a blood-corpuscle. These little bodies exhibit no spontaneous motion."
Pasteur began the examination of splenic fever by securing some of the blood from an animal dying from it. In the work before him he associated with himself M. Joubert, one of his former pupils. A drop of the blood sown in the water of yeast—the medium used for cultures by Pasteur at that time—produced myriads of the rods, the bacilli or microbes. A drop of this taken at the end of twenty-four hours, and placed in a fresh flask of the medium, again produced thousands of the bacilli. Pasteur found that guinea-pigs inoculated from the first flask developed the fever, and the same result followed when the inoculation was from the twentieth. He had proved, then, that splenic fever was produced by the bacilli, by living organisms only to be seen with a powerful microscope.
While working on the bacilli of splenic fever, Pasteur had isolated the bacillus of chicken cholera, had cultivated it and had inoculated chickens with it, developing the disease. He found that so long as the cultures were made from flask to flask within twenty-four hours, the virus of the disease, that is, the power of the bacilli to produce cholera in the fowls inoculated, remained the same and the fowl died. But he discovered that if a flask containing the bacilli were left exposed to the air for two weeks, and the fowls were then inoculated with bacilli from this flask, they became sick, but did not die. Following this up, he inoculated a hen that had recovered from a sickness so produced, with the bacilli in their strongest and most virulent form, and the hen showed no effect whatever. Then he took two hens, one fresh from the coop and the other well again after the sickness produced by the inoculation with the exposed bacilli, and inoculated both with the blood of a hen that was dying of chicken cholera. The first died, the second was affected. In other words, Pasteur had made the greatest discovery in physiology of this century. He had found it is possible to attenuate the virus of a virulent disease, and to use that virus so attenuated as a vaccine matter which will guard the animal vaccinated against the disease. He had taken Jenner's discovery, and proved it applied to other diseases besides small-pox.