The particular service of Johannes Müller to science was to make physiology broadly comparative. So comprehensive was his grasp upon the subject that he gained for himself the title of the greatest physiologist of modern times. He brought together in his great work on the physiology of man not only all that had been previously made known, carefully sifted and digested, but a great mass of new information, which was the result of his own investigations and of those of his students. So rigorous were his scientific standards that he did not admit into this treatise anything which had been untested either by himself or by some of his assistants or students. Verworn says of this monumental work, which appeared in 1833, under the title _Handbuch der Physiologie des Menschen_: "This work stands to-day unsurpassed in the genuinely philosophical manner in which the material, swollen to vast proportions by innumerable special researches, was for the first time sifted and elaborated into a unitary picture of the mechanism within the living organism. In this respect the _Handbuch_ is to-day not only unsurpassed, but unequalled." Müller was the most accurate of observers; indeed, he is the most conspicuous example in the nineteenth century of a man who accomplished a prodigious amount of work all of which was of the highest quality. In physiology he stood on broader lines than had ever been used before. He employed every means at his command--experimenting, the observation of simple animals, the microscope, the discoveries in physics, in chemistry, and in psychology. He also introduced into physiology the principles of psychology, and it is from the period of Johannes Müller that we are to associate recognition of the close connection between the operations of the mind and the physiology of the brain that has come to occupy such a conspicuous position at the present time. [Illustration: Fig. 56.--Johannes Müller, 1801-1858.] Müller died in 1858, having reached the age of fifty-seven, but his influence was prolonged through the teachings of his students. Physiology after Müller [Illustration: Fig. 57.--Ludwig, 1816-1895.] Ludwig.--Among the men who handed on the torch of Müller there has already been mentioned Ludwig (Fig. 57). For many years he lectured in the University of Leipsic, attracting to that university high-minded, eager, and gifted young men, who received from this great luminary of physiology by expression what he himself had derived from contact with Müller. There are to-day distributed through the universities a number of young physiologists who stand only one generation removed from Johannes Müller, and who still labor in the spirit that was introduced into this department of study by that great master. [Illustration: Fig. 58.--Du Bois-Reymond, 1818-1896.]