In regard to the experimentation and the valuable instruction thus acquired, it appears that Herbst was the first to rear muscle-flesh-worms, or encapsuled Trichinæ, in animals (1850); whilst Virchow was probably the first to rear and recognise sexually-mature intestinal Trichinæ in a dog (‘Deutsche Klinik,’ 1859, s. 430); yet, without doing injustice to others, it must be added that it remained for Prof. Leuckart to offer a full, complete, and correct solution of the principal questions relating to the source and mode of genesis of the flesh-worm (1860). Leuckart likewise did good service by disproving the erroneous views that had been put forth by Küchenmeister. Lastly, all these brilliant results culminated in the clinical observations of Zenker, who opened out a new epoch in the history of trichinal discovery. Professor Zenker was the first to detect the young in the act of migration, and he likewise primarily demonstrated the fact that the larval parasites were capable of producing a violent disease in the human body. [Illustration: FIG. 35.--Sexually mature _Trichina spiralis_; male. After Leuckart.] Never in the history of biological science have more valuable issues followed the method of experiment upon animals. Not only has human life been thus saved, but animal life also. State-medicine and sanitation have received an immense impulse. The good that has already resulted is simply incalculable; nevertheless, in the eyes of a set of ignorant fanatics who infest this country, all experiments “involving cruelty to animals” ought to be prevented at any cost. The further progress of biological science in England has hereby sustained a severe check. The _Trichina spiralis_ in its sexually-mature state is an extremely minute nematode helminth, the adult male measuring only the 1/18th of an inch, whilst the perfectly developed female reaches a length of about 1/8″. The body is rounded and filiform, usually slightly bent upon itself, and rather thicker behind than in front, especially in the males. The head is narrow, finely pointed, unarmed, with a simple, central, minute oral aperture. The posterior extremity of the male is furnished with a bilobed caudal appendage, its cloacal or anal aperture being situated between these divergent appendages. The penis consists of a single spicule, cleft above, so as to assume a V-shaped outline. The female is stouter than the male, bluntly rounded posteriorly, having the genital outlet placed far forward, at about the end of the first fifth of the long diameter of the body. The eggs measure 1/1270″ from pole to pole. The mode of reproduction is viviparous. [Illustration: FIG. 36.--Larval Trichina coiled within its capsule. After Bristowe and Rainey.]