These being the effects as exercised by compression on the bulbar centres, one must not omit to consider the results produced on the higher cortical centres. Anæmia is the feature and unconsciousness is the ultimate result, preceded by headache and drowsiness progressing on to stupor and coma. Intermediate between the stages of sleepiness and coma, one observes occasionally a stage of irritation--such as is pictured in many cases of typical middle meningeal hæmorrhage. In fatal cases the respiratory centre gives out first, the heart often beating for some time after all attempts at respiration have ceased. In a case recently under my care, respiration ceased during the process of trephining. The patient was kept ‘alive’ for three hours by means of artificial respiration, and under such mechanical breathing the patient retained a good colour and the heart worked well. So soon, however, as efforts were relaxed, the pulse became weaker and weaker until further artificial respiration again restored the balance. This process was kept up till it was realized that the respiratory centre was ‘dead’. From these facts, it may be assumed that the special symptoms of compression are dependent (_a_) on anæmia of the bulb--with corresponding cardiac, respiratory, and vaso-motor changes; and (_b_) on anæmia of the cortex--with unconsciousness. =Its symptomatology.= According to Kocher, the following are the four stages of compression:-- 1. _The stage of compensation._ A mild degree insufficient to seriously compromise the circulation. Cerebro-spinal fluid escapes into the spinal canal and some of the venous radicles are compressed. Some venous engorgement. Some headache, possibly some focal symptoms. Some mental dullness. 2. _Stage of beginning compression._ Beginning failure of the circulatory compensation. Headache pronounced, vertigo, restlessness, excitement or delirium. Objective symptoms of venous stasis--dilatation of the veins of the eye, both external and internal, œdema of the disk. Affection of the medullary centres, shown by a slowed pulse and a slight rise in temperature. 3. _Stage of fully-developed compression._ Widespread capillary anæmia. Medulla affected markedly. The period of vaso-motor regulation has set in with its high blood-pressure, and this, with its vagal quality, gives the pulse its bounding character. The rise in blood-pressure shows a definite rhythm. Also rhythmicities in respiration which may acquire the Cheyne-Stokes character. Rhythmic alterations in the size of the pupils, with alternate increase and decrease in the depth of stupor, so that the ‘up-wave’ causes the patient to moan, become irritable, and thrash about, whilst the ‘down-wave’ sees him completely comatose. Pulse is markedly slowed and the disks evidence pronounced ‘choking’. Reflexes are abolished, cyanosis extreme, respiration snoring.