“In order to resolve the highly important question of the tenacity of life of the Helminths and corresponding larval forms, I made since 1871 a very long series of experiments on the Cysticercus cellulosæ, which were published almost at the same time with others of the same kind, made by Dr Lewis in Calcutta. Towards the end of 1874 Mr Pellizzari, of Florence, disputed the results of the investigations which I had made known two years before, i.e. in 1872, and agreed with Dr Lewis, who had stated already that the Cysticercus exposed to a temperature of 55° C. can be held for dead after five minutes, and also with Dr Cobbold, who thought the temperature of 60° C. quite enough to kill it. But the characters he (Mr Pellizzari) relied upon, needing the exactness and precision required to enlighten and persuade in the most important scientific questions, gave rise to a mistrust in the most scrupulous amongst the men devoted to biological pursuits and to several hygienic measures on the part of the sanitary inspectors with regard to infected pork. Therefore, my conclusions, argued from the experiments made in 1871–72, were still those followed by the most important Italian cities, and approved in principle by the superior Board of Health in 1873. I expressed doubt then about the Cysticercus dying at a temperature lower than 100° C., and some person misconstrued these doubts, saying that I had contradicted myself in my work. However, as I could not assert they died at 80°–100° C., I only noticed the alteration of color and cohesion which happened in the Cysticercus exposed to various degrees of temperature, to the end that I might contribute usefully to the solution of the difficult question, and concluded that ‘if we could not be sure of the Cysticercus dying at 80°–100° C., it was certain at all events that they perished at 125° or 130° C.’ Not wishing to prejudice the question, I never said that they did not die at 80°–100° C., but simply stated that at this temperature we could not be certain of their death.
“Now, after a large number of experiments, I have been able to ascertain with exactness the lowest degree of temperature required to kill infallibly the Cysticercus and other parasites of animals. The means I made use of for this kind of investigation were Mr Schulze’s heating table, the neutral tincture of carmine, the tincture of hæmatoxylon, and breeding experiments.
“My method is founded essentially—
“(a) On the fact that the Cysticercus when it is fresh and is stretched and conveniently prepared in pure water, or in chloride of soda very much diluted, and afterwards brought gradually from the temperature of the ambient air to that of the body of higher animals and to degrees of heat still more elevated, until life is extinct, keeps moving to and fro with more or less energy throughout its body, using especially its suckers and proboscis.
“(b) On the greater imbibing power of the dead tissue generally, which is undoubtedly far more apparent in insects and plathelminths.
“(c) On the experiments made to ascertain the value of the two above-stated facts.
“If, after having prepared a Cysticercus, newly extracted from a pig in the way we have pointed out, we examine it with a microscope on M. Schulze’s heating table, we find that usually it begins to move after 30° or 35° C., and each moment with greater activity, especially after 38°, 40°, 42°, 44°, 45° C. The temperature being raised progressively, we see that the Cysticercus cellulosæ puts a stop to its movements occasionally at 45–46° C., seldom at 47° C., more frequently at 48° C., sometimes at 49° C.; and, in fifty and more experiments, only one Cysticercus was able to live on beyond 49° C., standing still at 50° C.
“As soon as it stands still the parasite is dead. In fact, if we lower again the temperature gradually to that of the ambient air, and if afterwards we raise it a second time, we pass through all the intermediate temperatures without the Cysticercus showing the least signs of life.
“But a more convincing proof of the death of the parasite is got from the greater imbibing power of the tissue when life is extinct, the same over the whole body of the plathelminths, and their larval forms. If we dip the Cysticercus alive with its head stretched in the neutral tincture of carmine or hæmatoxylon we can leave it there even two, four, eight, ten, or twelve hours and more, without the head coloring or a real imbibition taking place; this begins only after the Cysticercus is dead, so that if the Cysticercus is brought first to a temperature hot enough to kill it (with M. Schulze’s tables to one of 48°, 49°, 50° C.) and dipped afterwards in the above-mentioned tinctures, it colors intensely in less than 45°, beginning from the head, and onwards to the extremity of the cyst of the tail. The head colors more intensely and rapidly than the neck, as it is covered with very numerous calcareous corpuscles, which are not met with so frequently in the remaining part of the body.
“Cysticercus cellulosæ of the pig, and that of the Tænia mediocanellata of the calf, brought gradually to a final temperature, the first of 50° C., and the second of 44°, 45°, and 47° C., and then swallowed alone, or with a piece of butter or crumb of bread, never produced the Tænia in the valiant students who voluntarily undertook to make the experiment of swallowing them.