It would be a loss of time to enumerate the different objections which have been urged against the validity of this test, on various grounds, many of which admit of an easy answer. It is sufficient to state that experiments, subsequent to those of _Plouquet_, by _Haartman_,[81] _Struve_,[82] _Schmitt_, and _Lecieux_,[83] have shewn that no constant relation between the weight of the lungs and that of the body, under the circumstances above mentioned, can be established. The reason of which, as _Dr. Hutchinson_ has justly observed, without considering the influence of variation in the original construction of the body, is sufficiently accounted for, by the great diversity in the manner in which respiration is established in new-born infants. We have already stated that, in a great proportion of them, it is but gradually and slowly effected; and that several days even may elapse before the lungs are fully dilated. _Dr. Gordon Smith_[84] is disposed to believe that data might be obtained for a just conclusion upon this point, if practitioners would institute farther inquiry into the subject; and, with this impression, he has been induced to enter more fully into the history of the test, than we deem necessary, believing as we do, that it can never afford evidence sufficiently decisive for practical application. _Daniel_ has proposed a modification of _Plouquet’s_ test, but which is more objectionable even than that which he professes to improve. The same physiologist considers that an inference may be drawn from the increased circumference of the thorax, and the vaulted appearance it assumes after respiration. The objections urged by _Dr. Hutchinson_ to these latter indications appear to us to be unanswerable; the circumference of the thorax, says he, varies so much in infants of the same age and sex, both absolutely and in proportion to other parts of their body, that it cannot be possible to obtain any decisive evidence from it. The vaulted appearance of the chest is almost equally fallacious in the generality of cases, or else it is devoid of utility; because the figure of the thoracic parietes is not much changed until respiration has been fully established, and then we have other and more certain means of detecting its existence. Besides which, it appears from the experiments of _Schmitt_, that the thoracic parietes were distended outwards by artificial insufflation after death, as much as they are by actual respiration as it occurs in the new-born infant. With these remarks we shall dismiss the subject of _Docimasia Pulmonaris_, and proceed to inquire whether the structure of the heart is capable of affording any useful indications. There can be no doubt but that, some time after birth, we shall find on inspecting the heart, evident marks of the altered course of the circulation. The _foramen ovale_ will be closed, and in extending our examination, we shall find that the _ductus