1. The normal anatomy of the intervertebral disc of immature rabbits is described.

2. An account is given of the changes that occur after an operative incision in the ventral part of the intervertebral discs of rabbits which allowed the escape of the nucleus pulposus. The account is based on observations made on fifty-five young animals killed at intervals during the twenty-five months after operation.

3. The superficial part of the wound in the annulus heals rapidly by active fibrosis. Thereafter there is a chondrification of the ventral region of the disc, followed by ossification. A prominent bony ridge ultimately ankyloses the vertebrae adjoining the disc.

4. The site of the nucleus pulposus is eventually occupied by a dense pad of fibrocartilage. A tongue of this tissue projects into the deep median part of the wound which remains unhealed.

5. A hypothesis is submitted regarding the mechanism of rupture of the annulus fibrosus and prolapse of the nucleus pulposus in man; this hypothesis is based in part on the observations of lesions in discs not subjected to operation.

One hundred and sixty-four cases of intramedullary nailing of the long bones have been studied with special reference to the difficulties and complications encountered.

There was one death not attributable to the method.

Two cases of pulmonal fat embolism and one case of thrombosis occurred, all in fractures of the femur.

The lessons we have learned from our mistakes can be summarised as follows:

1 . The method requires technical experience and knowledge and is not suited to inexperienced surgeons or surgeons with little fracture material at their disposal.

2. Intramedullary nailing should only be used in fractures to which the method is suited. In general, comminuted fractures or fractures near a joint are unsuitable.

3. Open reduction is preferable to closed methods.

4. The nail should never be driven in with violence. It should be removed and replaced with a new one if difficulty is encountered when inserting it.

5. In fractures of the femur the nail should be driven in from the tip of the trochanter after careful determination of the direction.

6. The nail should be introduced only to the level of the fracture before exploring and reducing the fracture.

7. Distraction of the fragments must be avoided.

8. If the nail bends it should be replaced by a new one, at least in femoral fractures.

9. If union is delayed, the fracture should be explored and chip grafts of cancellous bone placed around it.

10. Improvised nails or nails which are not made of absolutely reliable material should never be used.

11 . Make sure that the nail is equipped with an extraction hole for removal.

1. An attempt has been made to rationalise the selection of the site of amputation for gangrene in primary peripheral vascular disease.

2. There is a good chance of the survival of a below-knee stump if the circulation in the skin of the proposed flaps appears adequate clinically, and if the blood supply to the muscles is obviously good at amputation.

3. If the popliteal pulse is present before operation, below-knee amputation should succeed. The absence of a popliteal pulse, however, does not exclude below-knee amputation.

4. Below-knee stumps should be about four inches long in amputations for peripheral vascular disease.

5. Tests for determining the state of the circulation are also necessary before choosing the level for above-knee amputations.

This is the first time that the principle of the mould—the principle of guiding the repair of nature for the purpose of recreating a destroyed or damaged structure, has been applied to surgery. The evolution of the method to its present encouraging stage is the result of the co-operative, professional family spirit of the Massachusetts General Hospital. We all share in it. We share it with the general surgeon because of his contributions to surgical technique. We share it with the "medical man" because of his pre-operative and post-operative care of the patient; because of his guidance as to when, and when not, to operate; and because of the many friendly arguments which are productive of so much good. We share it with the anaesthetist because of his clinical judgment of the patient, his selection of anaesthetic agent, and his continuous, conscientious administration of the anaesthetic throughout the operation.

I am going to change from "we" to "I." I owe so much to my assistants, from the first to the last: Bill Rogers, Eddie Cave, George Van Gorder, Paul Norton, Milton Thompson, Otto Aufranc, and Carroll Larson. I want to thank them all for helping to carry the load, for remembering the things that I forgot, and for making helpful suggestions which often led to improvement in surgical technique or to the construction of a useful instrument. I want to pay tribute to the staff of the Orthopaedic Service of the Massachusetts General Hospital and to thank its members for kindly scepticism, constructive criticism, and neverfailing loyal support.

The subject of this lecture, "Evolution of Mould Arthroplasty of the Hip Joint," is appropriate for a Moynihan lecture. It is not the work of one man alone. It is the work of one man, supported by a co-operative, helpful, and friendly hospital staff. This is what Lord Moynihan strove so hard to bring about at a time when surgeons viewed one another as rivals. To quote Dr William Mayo: "It is to Lord Moynihan's everlasting credit that, largely as a result of his unceasing efforts, surgeons came to consider themselves as fellow-workers in a cause."