Ehrenberg.--Observations in this domain kept accumulating, but the next publication necessary to mention is that of Ehrenberg (1795-1876). This scientific traveler and eminent observer was the author of several works. He was one of the early observers of nerve fibres and of many other structures of the animal frame. His book of the protozoa is a beautifully illustrated monograph consisting of 532 pages of letterpress and 69 plates of folio size. It was published in 1836 under the German title of _Die Infusionsthierchen als Vollkommene Organismen_, or "The Infusoria as Perfect Organisms." The animalcula which he so faithfully represented in his sketches have the habit, when feeding, of taking into the body collections of food-particles, aggregated into spherical globules or food vacuoles. These are distinctly separated, and slowly circulate around the single-celled body while they are undergoing digestion. In a fully fed animal these food-vacuoles occupy different positions, and are enclosed in globular spaces in the protoplasm, an adjustment that gave Ehrenberg the notion that the animals possessed many stomachs. Accordingly he gave to them the name "Polygastrica," and assigned to them a much higher grade of organization than they really possess. These conclusions, based on the general arrangement of food globules, seem very curious to us to-day. His publication was almost simultaneous with the announcement of the cell-theory (1838-39), the acceptance of which was destined to overthrow his conception of the protozoa, and to make it clear that tissues and organs can belong only to multicellular organisms. Ehrenberg (Fig. 31) was a man of great scientific attainments, and notwithstanding the grotesqueness of some of his conclusions, was held in high esteem as a scientific investigator. His observations were accurate, and the beautiful figures with which his work on the protozoa is embellished were executed with such fidelity regarding fine points of microscopic detail that they are of value to-day. Dujardin, whom we shall soon come to know as the discoverer of protoplasm, successfully combated the conclusions of Ehrenberg regarding the organization of the protozoa. For a time the great German scientist tried to maintain his point, that the infusoria have many stomachs, but this was completely swept away, and finally the contention of Von Siebold was adopted to the effect that these animals are each composed of a single cell. [Illustration: Fig. 31.--Ehrenberg, 1795-1876.] In 1845 Stein is engrossed in proposing names for the suborders of infusoria based upon the distribution of cilia upon their bodies. This simple method of classification, as well as the names introduced by Stein, is still in use. From Stein to Bütschli, one of the present authorities on the group, there were many workers, but with the studies of Bütschli on protozoa we enter the modern epoch.