Every method of physical exploration can yield information only with regard to physical conditions, but for the establishment of the anatomic and physiologic significance of which other data will be required. It should hardly be necessary to add that the observations must themselves be in the first place above suspicion. Here, as in the application of all methods of precision, are demanded the two essentials of correct perception and equally logical interpretation, and both of these bespeak a certain foreknowledge. While the large possibilities for diagnostic usefulness of the X-rays were early appreciated, it soon became recognized that the results obtained were susceptible of varied interpretations, in accordance with the skill and the experience of the observer and the opportunities for the development of what, for want of a more convenient term, may be designated "artefacts."
Some of these sources of error are pointed out in a communication presented to