This difference between the physical organism and society is fundamental and essential. It is far more striking than the superficial likenesses ingeniously adduced by Mr. Spencer. His analogy tends to obscure the real nature of social relations. Unless used with cautious qualifications it "suggests false and one-sided views" and thus hinders the progress of sociology. The biological analogy has, it may be conceded, a certain value as a convenient way of describing some of the aspects of social structure and growth. It may aid the student to comprehend certain facts, but, if followed blindly, it will lead him to overlook other facts of even greater importance. The biological analogy has been carried to absurd lengths by some writers. There is wearisome enumeration of social aggregates and organs, and exhaustive description of the social nervous system. We learn that the individual may be either a communicating cell or a terminal cell, otherwise known as an end organ. The girl in the central telephone office acts as a communicating cell when she telephones to Mr. Smith a message from Mr. Brown. "But when, Mr. Smith having asked her the exact time by the chronometer in the exchange, she looks at the dial and reports her observation to him, she is primarily a terminal cell or end organ."[41] The lookout man at sea, on the other hand, is invariably an end organ. This is far-fetched and fanciful. To clothe mere commonplaces in the borrowed rags and tags of biological terminology is not social science, nor does it aid one to get a correct conception of social reality. [Footnote 41: Small and Vincent. Introduction to the Study of Society, p. 218.] The unsettled state of sociological thought which has been here set forth is a natural result of the peculiar difficulties that stand in the way of the social sciences. These have been described by Mr. Spencer with great fullness of illustration.[42] They arise from three sources--namely, (1) from the intrinsic nature of the facts dealt with; (2) from the natures of the observers of these facts; and (3) from the peculiar relation in which the observers stand toward the facts observed. [Footnote 42: Herbert Spencer. Study of Sociology, chaps. iv to xii.] 1. In the first place the peculiar nature of social phenomena is such as to render scientific observation difficult. They are not of a directly perceptible kind like the phenomena which form the subject-matter of the natural sciences. Quantitative measurement and experiment are not possible. Social facts "have to be established by putting together many details, no one of which is simple, and which are dispersed, both in space and time, in ways that make them difficult of access."